In the reactionwhere V and 'b' are the van der Walls parameters which depend upon nature of gas.Significance of constant ‘V : The constant 'V is excluded volume per mol of a gas.Its units are L ${{mol}^{-1}}$ The volume of ‘V is four times the actual volume of the molecules. Significance of constant 'a' : It gives the ideal of magnitude of attractive forces between the gas molecules. Its units are atm ${{L}^{2}}$ ${{mol}^{-2}}$. Larger the value of 'a' Larger will be the intermolecular attraction among the gas molecules.